In some Three-Dimensional Integrated Circuits (3DIC), device dies are first bonded to an interposer, which is further bonded to a package substrate to form a package. The heat generated in the device dies during their operation needs to be dissipated. In the conventional structures, to dissipate the heat, the substrates of the device dies are attached to a heat spreader, which has a size larger than the sizes of the device dies and the package substrate. Accordingly, the heat generated in the device dies is spread to a larger area. A heat sink is attached to the heat spreader to dissipate the heat conducted to the heat spreader.
The attachment of the device dies to the heat sink is through a Thermal Interface Material (TIM), which may include an epoxy-based material. In addition, some thermal conductive materials such as silicon particles may be mixed in the epoxy-based material to increase the thermal conductivity of the TIM. The attachment of the heat sink to the heat spreader is through another TIM. Due to the use of two TIMs, the efficiency in the heat dissipation is reduced.